Long vowels, marked with an acute accent or a circumflex, are longer
than short vowels (duh) and always make a heavy syllable (i.e. we don’t
include the rules to move stress to the previous syllable). In Quenya,
⟨é⟩ and ⟨ó⟩ are “tenser and ‘closer’” than the short vowels, according
to Appendix E of The Lord of the Rings, while in Sindarin they’re
supposed to be the same; the phonemes we inherit from Latin seem to
reproduce this reasonably well for Quenya, and for now we use them for
Sindarin too, which works nicely for the most common Sindarin word with
a long o, “Lothlórien” (because Lórien is actually a Quenya name, and
therefore I assume *that* ⟨ó⟩ should actually be /o/ and not /ɔ/). I
might adjust the phonemes later (at which point Lothlórien will
presumably have to go in sjn_list).

In Elvish languages, ⟨ch⟩, ⟨dh⟩, and ⟨th⟩ count as single consonants for
the purposes of stress, since they represent single letters in the
original scripts. The easiest way to implement this is to replace them
with single letters at the beginning – ⟨ð⟩ for ⟨dh⟩ and ⟨þ⟩ for ⟨th⟩ are
natural, and ⟨x⟩ for ⟨ch⟩ also makes some sense, though it means we need
to replace real ⟨x⟩ first (it’s not mentioned in Appendix E of The Lord
of the Rings, but does occur in some Quenya words, notably Helcaraxë).
Real ⟨x⟩ is pronounced like /ks/, but of course we need to spell that as
⟨cs⟩, since ⟨k⟩ does not occur in Elvish languages.

The Elvish languages have the same general stress rule as Latin [1]:
stress falls on the penultimate syllable if that is heavy (contains a
long vowel, a diphthong, or a vowel followed by two or more consonants),
otherwise on the antepenultimate syllable. For Latin, espeak-ng
implements this by declaring “penultimate syllable” as the general
stress rule in espeak-ng-data/, and then adding rules in dictsource/
that match light syllables and move the primary stress to the previous
syllable, i.e. the antepenultimate one. We use the same basic principle
for the Elvish languages here (but using the terms “heavy” and “light”
rather than “weak” and “strong” like in the Latin files).

Note that this doesn’t fully implement the stress rules yet: we have no
concept of diphthongs, long vowels aren’t really properly handled yet,
and we also still count ⟨ch⟩, ⟨dh⟩, ⟨th⟩ as two consonants rather than
one as it should be. This will be improved separately (I prefer doing
this in small incremental steps).

[1]: https://menegroth.github.io/stress-in-sindarin.html

Copied from Sindarin with only a few changes so far: initial ⟨i⟩ is not
special, ⟨qu⟩ exists, and ⟨y⟩ is a consonant.

This prepares the languages of Quenya and Sindarin, setting up their
infrastructure without declaring a lot of rules yet – just enough for
“Eä” (a Quenya word, but I can’t think of a similarly simple one for
Sindarin). Phonemes are inherited from Esperanto for now.